"Get a room."
Do you know anyone who's getting a hotel room for prom? It always kind of amazes me when people's parents let them do that -- would yours? I can't picture mine having let me back then; I didn't even bother to ask.
Anyway, if you do have laid-back parents, take a lesson from Eric on That '70s Show and spring for a decent room instead of one with a stain on the bed and a gross bathroom. So not prommy.